Study: Monarchs Use Milkweed as Preventive Medicine—but Climate Change May Wreck the Pharmacy

This article discusses how monarch Butterflies will be deleteriously affected by climate change. Rising CO2 levels could upset the delicate relationship between the butterflies and their parasites.

Most people know that monarch butterflies can’t exist without milkweed. As caterpillars, the monarchs feed on milkweed plants exclusively, absorbing the milkweed’s poisons in order to ward off birds and other predators. On their epic migration across the North American continent, the butterflies also lay their eggs on these plants, relying on the noxious taste of the leaves to keep their brood safe from grazers while simultaneously providing a buffet for the next generation when it hatches.

But milkweed plays another role in the lives of monarchs that goes largely overlooked. Some of the compounds produced in the plants’ leaves act like medicine for the butterflies, both protecting them against parasites, like the protozoan Ophryocystis elektroscirrha, and helping them cope with parasitic infections when they do occur.

Unfortunately, a new study published in the journal Ecology Letters finds that as carbon dioxide levels rise in the atmosphere, the most medicinal of those milkweed plants start to lose their juju. “Our study shows that a loss of medicinal protection caused by elevated CO2 makes the parasite more virulent,” says lead author Leslie Decker, an ecologist now at Stanford University. (The research was part of Decker’s doctoral dissertation at the University of Michigan.)

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